# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Historical question
From: Alexandre Eremenko
Date: 2004 Oct 23, 19:04 -0500

```I have a conjecture explaining the misterious paragraph of Norie.
Before I state it, let me continue that citation a bit:

"...having a good Quadrant to take the altitudes,
and a Sextant to observe the distances.
Let the observations be taken in the following order,
noting the times by a watch: 1, the altitude of the Sun
or Star; 2, the altitude of the Moon; 3. any number of distances;
4, the altitude of the Moon; 5, the altitude of the Sun or Star".

First, let us assume that a navigator who could afford a
good sextant (worth about 20 pounds sterling
at the time when
gold was 4 pounds 8s per ounce).
would also have a wooden quadrant, as a backup, or to permit
his assistants to handle. (Its price was about 1/4 of that
of a sextant if I remember correctly). So the presence
of the second
instrument on board is not surprising.

Second, we have to take into account that
a) The reading of those sextants was much slower than of
the modern ones. They had a long Nonius (Vernier), permitting
b) It takes some time to catch both bodies (or a body
and the horizon)
in
the filed of view.

Then using both instruments (if you already have them!)
for this sort of observation makes a sense. All distance
observations, made by the Sextant, with maximal precision
are not interrupted by altitude observations.
does not have to be reset.

This permits the series of observations in a quick sequence.
time.

Notice, that the whole procedure is designed to minimize
the total time of the observation (see the discussion on Averaging).

Now let me continue the citation a bit further:

"Now add together the distances, and the times when they are taken,
each of which being divided by the number observed...."

Alex.

```
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